The US military has released video footage to justify Tuesday's controversial aerial bombing on the Afghan border in which 11 Pakistani soldiers died.

The footage - grainy monochrome images taken from a surveillance drone - is unlikely to quell Pakistani anger about the incident at Gorparai, a remote outpost on the northern border with Afghanistan.

The Pakistani military described the attack as "completely unprovoked and cowardly" and the prime minister, Yousaf Raza Gilani, condemned it in parliament.

The heavily edited film gives a taste of the mountainside battle but offers no conclusive evidence to support the American version of events.

The opening sequence shows half a dozen figures, identified as "anti-Afghan forces", perched on a ridge, firing their guns and rocket-propelled grenades. A voice says they are fighting with a coalition reconnaissance patrol, which is not visible.

The location is identified as being 200 metres inside Afghan territory. No border markers are visible to confirm this.

After 45 minutes of combat the fighters are seen scurrying back down the hill. The surveillance drone - described a "Warrior Alpha unmanned aerial system" - follows them through the ravines and, it says, into Pakistan.

Three hours after the initial contact, the video shows three bombs being dropped on the militants, killing at least five people.

After each strike the voice stresses that the Warrior Alpha "zooms out to ensure there are no structures or outposts within the impact area" - the US justification that it did not target the Pakistani border post at Gorporai.

"Every indication we have is that this was a legitimate strike against forces that had attacked members of the coalition," said the defence department press secretary, Geoff Morrell, in Washington.

The Pentagon said that 12 bombs were dropped but it was too early to know whether one of them killed the 11 Pakistani soldiers.

The Pakistani military offered a very different version of events.

The military spokesman, Major General Athar Abbas, said that trouble started at 10am on Wednesday morning when a group of Afghan soldiers occupied a border position on a contested tract of land.

After complaints from Pakistani soldiers they agreed to retreat into Afghanistan but were attacked by insurgents. The Afghans called in coalition air support, he said.

During the air strikes several bombs were dropped on the Pakistani border post, where 50 soldiers were stationed, he said. Some landed on the main building and others on outlying bunkers.

Eleven Pakistani soldiers were killed - an army officer and 10 men from the paramilitary Frontier Corps - and seven injured he said. About 10 others fled their post and retreated.

The Pakistanis did not open fire at any stage, he said: "As far as our side is concerned, there was no ground engagement with any forces."

Gen Abbas declined to comment on the US videotape, saying only that the army was "considering its response".

The controversy adds friction to an already troubled relationship. The US is impatient at Pakistani attempts to negotiate peace deals with militants in the tribal areas, which it feels only give the insurgents time to reorganise and reequip.

American pushiness angers Pakistanis who feel they have paid a high price for cooperating in President George Bush's "war on terror". Since 2002 more than 1,000 Pakistani soldiers have died in the tribal area, where the fight against militancy has become known as "America's war".

Pakistanis blame American drone strikes against al-Qaida targets in the tribal belt for stirring a militant backlash that has sparked a spate of suicide bombings in the major cities over the past year.

That anger has also hurt President Pervez Musharraf, whose friendship with Bush has caused him to be derided as "America's dog" in protest rallies.

US officers are due to start a training programme with the Frontier Corps later this year. Abbas declined to comment on whether the Gorparai bombing would affect those plans.

Pakistan's Dawn newspaper blamed the incident on a lack of coordination on the border and deep distrust between the Paksitani and Afghan governments.